The present disclosure relates generally to thermally activated strong acids. More specifically, in certain embodiments, the present disclosure relates to compositions capable of generating strong acids downhole and associated methods.
Acid treatments using aqueous acidic solutions commonly are carried out in subterranean formations. These acid simulations may be used to accomplish a number of purposes. Such purposes may include increasing or restoring the permeability of subterranean formations so as to facilitate the flow of oil and gas from the formation into the well. The acid treatments may be used to remove formation damage along as much of the hydrocarbon flow path as possible and/or to create new flow paths as in matrix acidization.
Generally, in acidizing treatments, aqueous acidic solutions are introduced into the wellbore or subterranean formation under pressure so that the acidic solution flows into the wellbore or pore spaces of the formation. Within the wellbore, the acidic solution may also remove wellbore damage and filter cake. Within the near-well formation, the acidic solution may remove near-well formation damage and other damaging substances. In the near-well formation, the acidic solution may react with acid-soluble materials contained in the formation which results in an increase in the size of the pore spaces and an increase in the permeability of the formation. This procedure commonly enhances production by increasing the effective well radius. Examples of such methods are disclosed in U.S. Pat. No. 7,795,186, the entirety of which is hereby incorporated by reference.
Although acidizing a portion of a subterranean formation can be very beneficial in terms of permeability, conventional acidizing systems have significant drawbacks. One major problem associated with conventional acidizing treatment systems is that deeper penetration into the formation is not usually achievable because, inter alia, the acid may be spent before it can deeply penetrate into the subterranean formation. Another problem associated with acidizing subterranean formations is the corrosion caused by the acidic solution to any metal goods (such as tubular goods) in the well bore and the other equipment used to carry out the treatment. For instance, conventional acidizing fluids, such as those that contain organic acids, hydrochloric acid or a mixture of hydrofluoric and hydrochloric acids, have a tendency to corrode tubing, casing, and equipment both on the surface and downhole, especially at elevated temperatures. Another problem is that when acids are pumped into a well, they may cause scale to flake from the upper wellbore and settle and plug the well at a lower level. Another problem associated with conventional acidizing systems is that they can pose handling and/or safety concerns due to the reactivity of the acid.
Various methods of generating a thermally activated acidizing solution based on latent organic acids such as through the use of hydrolysable esters have been previously developed. These methods suffer from the limitations of generating an organic acid, which by their nature, is a weak acid that may only partially disassociate in a solution. This may limit the dissolving power of the solution and preclude the ability to generate silica dissolving acids such as hydrofluoric acid from fluoride salts.
It is desirable to develop a method acidizing a wellbore or a subterranean formation using a solution that generates a strong acid that does not suffer from any of these conventional drawbacks.